Pen cap



FIG. 1 is a top view of the pen cap.

FIG. 2 is a bottom view thereof.

FIG. 3 is a front view thereof.

FIG. 4 is a left side view thereof.

FIG. 5 is a right side view thereof; and,

FIG. 6 is a rear view thereof.

The broken line in FIG. 2 are for environmental purposes only and form no part of the claimed design. 

The ornamental design for a pen cap, as shown and described. 